Proper sun protection is important to prevent skin cancer, photoaging, and phototoxic reactions. The first thing you need to know about selecting a sunscreen is two concepts: Sun Protection Factor (SPF) refers to the ratio of the amount of energy required to produce minimal erythema on skin coated with sunscreen protection, to the amount of energy required to produce the same degree of erythema on skin without any protection. Simply put, it is the skin against ultraviolet rays (mainly UVB) times. PA indicates that the sunscreen products on the UVA defense ability, its defense effect is distinguished into three levels, PA + that can delay the skin tanning time of 2 to 4 times, PA + + + that can delay 4 to 8 times, PA + + + ten that can delay more than 8 times. Generally speaking, the sun protection index and the effectiveness of protection is not a linear relationship. Therefore, it is not the greater the SPF the better. The FDA (U.S. Food and Drug Administration) confirms that products with a SPF greater than 50 provide only slightly enhanced UV protection, so there is no special significance. SPF15/PA++ sunscreen products are often recommended for daily use. Many cosmetics today, such as BB creams, CC creams, and barrier creams come with a medium level of sun protection and are more popular with women. SPF30/PA+++ or higher sunscreen products are recommended for people who work outdoors, play sports, or engage in recreational activities. For those who need to be exposed to UV rays for long periods of time, such as at the beach, skiing, or driving for long periods of time, sunscreen products with SPF 50/PA+++ can be used.